In preparation for Lion, I want to make a bootable clone of my system to an external harddisk. I use TimeMachine, but I want to be sure I have a running backup.

Of course, there is much stuff on my system which doesn't need to be secured. This includes ~/Library/Caches and especially the installation of the developer tools (/Developer). To save space, I don't want to clone these.

Which tool can I use to do that? I have always cloned my harddisks with Disk Utility, but you obviously can't exclude directories with it.